Science explained with humor, analogy, and pop culture. (Because sometimes you just wanna understand a thing…)

The Zodiac is a Month Off

The zodiac circle, because nobody puts Babylon in a corner…

Babylonians Jotting Down the Zodiac

Picture yourself as an ancient Babylonian 3,000 years ago.

Babylon: “We also do gardening…”

You’re basking in the genius of your culture, as you have a calendar with 12 months that’s based on the lunar phases – ah, so very clever. But how to make sense of the rest of the world and the people around you?

Well, the animal-shaped star constellations of course! Thus, the zodiac signs and their influence was born.

Last month’s blog. Those were good times.

Just how we know it today, except now we know that there’s no science behind horoscopes (read more about the lack of effect of the celestial in Mercury is in Retrograde, Again).

But that doesn’t take away the fun! You get to keep all the fun and leave behind all the psychoses, leaving more time for learning the infinitely cooler history.

NASA Screws With Us All?

“You know what’s even more fun” thought NASA, “dropping a Babylonian big bang bomb on people who are obsessed with their horoscopes!” Well, not really. In fact, it was only in an obscure NASA kids’ blog somewhere that it was casually mentioned that there are actually 13 zodiac signs (not 12), and they aren’t on the dates we think they are. The Internet somehow caught celestial wind and exploded.

NASA had to actually issue a statement that they didn’t change anything, they just did the math. Sigh. We have arguably the best science agency in the world, must we embarrass ourselves in front of them on a constant basis? The cardio they must get from all the eye rolling…

So let’s redeem ourselves and look at the anthropology and the science! First, what is the zodiac exactly? Let’s separate the it’s-a-things from the not-a-things.

The Zodiac is an Actual Thing

Think of the Earth’s orbit around the sun. Think of all that 2D space between the Earth and the sun at any given time as a plane. This is called the ecliptic, because of the ecliptic orbit of the Earth.

Now, encircle that plane with a belt. Printed on that belt are all the constellations we associate with ‘our signs’. This area is called the zodiac (literally-ish, ‘circle of animals’). The idea is that it takes a month for the Earth to go by each one.

Well, that would be true except that the Babylonians kinda fudged it.

Because fudge!

See, the constellations stubbornly refused to fit into 12 nice sections. They overlapped all over the place, took over or under a month to pass, but even worse, there were too many.

Their calendar had 12 months, but there were 13 prominent signs. What to do? ehhh….let’s just sort of forget one.

The mystery sign? Ophiuchus (oh-fee-EW-kus), or serpent-bearer. It’s tragic backstory is a dude who is, wait for it, …holding a serpent (Serpentarius). All the other details are in debate and depend on which cultural mythology you go with.

Ophiuchus assures us that he’s a cold-hearted snake, look into his eyes…

Yep, there are millions of snakey-holdy personalities out there that are being completely unrecognized. #IAmASnakeyWoman #SignsUp #ImWithSer

But that’s not even why the zodiac is a month off from what we’ve all been told. To understand that, we have to understand how we calculate a year.

What Makes a Leo a Leo

The way it works is, if you’re say, a Leo, that’s because you were born when the sun was blocking the view of the constellation Leo from Earth.

Here, from the POV of Earth, the sun is blocking Scorpio. If you’re born in this time, you are associated with the arachnid terrorist of nature’s nightmares. Congrats!

(Why pick the blocked constellation? Well, the Babylonians also thought that the sun revolved around the Earth, so it made more sense in that context, as the sun would be ‘in’ Leo when you were born).

3000 years ago, the sun blocked Leo from about July 23 to August 22nd. But now, the sun blocks Leo from about August 10th to September 16th. Why? Because we judge years base on seasons, not star position.

How To Measure a Year

Turns out there are two different ways you can measure a year, by the stars or by the seasons.

In what’s called a sidereal year (sid-EAR-ee-uhl), we would say that the year begins anew when the position of the earth via the stars is the same as it was in the last orbit. But instead, we actually use a very similar but slightly different measurement, called a tropical year. It works like this:

Remember that the earth doesn’t orbit the sun along its equator, but that its axis is tilted.

Winter solstice is when the north pole is not speaking to the sun right now.

Let’s say we start the year at winter solstice. This is the shortest day of the year (in the northern hemisphere). In other words, when the tilt of the earth’s axis makes it so the north pole points directly away from the sun.

However, the Earth’s axis is actually wobbling like a dreidle when it’s about to fall.

This axis wobble is very slow (unlike the insufferably consistent spin at the ending of Inception, (or IS it?)).

Curse you Leo! Who isn’t even a Leo, but an arachnid terrorist of nature’s nightmares, who shall not be named.

It takes 26,000 years to make a full cycle wobble (precession is the actual term).

However, because it’s changing, the time when that north pole is facing away from the sun is different every year.

The winter solstice is 20 minutes earlier than last year’s. Not impressive, I know, you can space out for longer periods. But these little catnap bits of time adds up after 3,000 years. To about…a month. Therefore, when you were actually born, the sun was blocking a totally different zodiac sign than it was in the Babylonian’s time.

Current Dates of the Zodiac

But this is a crisis!! How will you answer to the next drunken hit-on who asks “What’s your sign?” Fear not with this handy chart, adjusted for the 3000 years, and the approximate time the sun actually blocks it:

Ophiuchus crushes Scorpio. Centuries of bitterness take its toll

Notice that today’s Scorpio only lasts for a week! The rest of the time we thought we were in Scorpio, we’re actually in Ophiuchus! Ah, but this makes sense.

If you look at the whole constellation picture, Ophiuchus is not only wrestling down a snake, but, as an extra diss, crushes Scorpio with his foot.

Your Horoscope is Not a Thing

I was born June 22, so I thought I was a Cancer. I’m now Gemini! Meaning instead of the itchy STD crab symbol named after a horrible disease (or a general term for prevalent scourge), I’m actually a Gemini, a couple of nude twinsees brothers with, admittedly, a prettier name.

From sixty-nining to Stonehenge. Improvement?

How much difference does this make? I’m sure I’ll feel just like Julia Sweeney reading her new horoscope – “I was astonished to find that it was ALSO totally me!”

photos created by me or in the public domain EXCEPT:
Leonardo DiCaprio – photo by Colin Chou, CC by SA 3.0